LED-based (retrofit) lamps are used more and more in home buildings and offices. Besides their high efficiency they also attract consumers due to new design features, different color temperatures, dimming ability etc.
To fit LED lighting to existing mains lighting fixtures, each LED light unit makes use of a converter circuit, for converting the AC mains into a DC drive signal, and also for reducing the voltage level.
The converter circuit typically comprises a rectifier and a switch mode power converter. One example of switch mode power converter is a ringing choke converter (RCC) based power converter. An RCC based buck converter is a typical self-oscillation converter in which the cyclic operation of the switching is self-controlled, and is widely used as a low cost LED driver. Other examples of the power converter are IC-based converters.
Current drivers are generally designed to operate with a specific mains input, generally 120V or 230V mains input voltage. There are now increasing demands for more flexible systems which can operate with different mains voltages, such as any AC input voltage between 120 and 277 V.
To provide a driver which can function over this input voltage range, designs are based on a professional IC with a MOSFET transistor control. This gives rise to a high system cost.
There is therefore a need for a lower cost LED driver suitable for a wide range of input mains voltages, and preferably of low cost, such as based on a self-oscillation architecture, such as an RCC architecture.
In a typical self-oscillation converter, the switch is controlled by an oscillated element such as an inductor. More specifically, the control terminal of the switch is provided with current/voltage by the oscillated element.